Performance of the "factor requirement test" for Haemophilus involves the:

Question

a. inoculation of unsupplemented media with a light suspension of the organism and placement of X and V factor disks on the agar surface.
b. inoculation of liquid media, unsupple-mented and supplemented with X and V factors.
c. detection of the presence of enzymes that convert <-aminolevulinic acid (ALA) into porphyrins.
d. growth of the organism in the presence of bacterial species that produce X and V factors as metabolic byproducts.

Answer 1

A
Traditional identification criteria include the requirement for X and/or V factors for growth. To establish X and V factor requirements, disks impregnated with each factor are placed on unsup-plemented media, usually Mueller-Hinton agar or trypticase soy agar, that has been inoculated with a light suspension of the organism. After overnight incubation at 35°C in ambient air, the plate is then examined for growth around each disk. Many X factor–requiring organisms are able to carry over enough factor from the primary medium to give false-negative results (i.e., growth occurs at such a distance from the X disk as to falsely indicate that the organism does not require the X factor).